From DE-OS 35 35 843, for example, it is known to estimate parameters by using the measured speed of a wheel and the measured brake pressure in successive sensing times . . . (T-1), T, (T-1) . . . by means of a difference equation and by using known identification algorithms. These parameters are used to determine estimated values .mu..sub.(t) for the friction coefficient between tire and road. The .mu.-values serve to determine the slope of the slippage curve ##EQU1## in the operating point and can be used in an anti lock brake control to achieve an optimal control. The slope K.sub..mu. of the .mu.-curve serves as a control value, and the brake pressure is controlled such that K.sub..mu. corresponds to a small, positive value. The slippage selected is always one that is to the left of the maximum (on the stable portion) of the .mu.-slippage curve, however, very close to the maximum.